Self-Supporting Nanoporous Copper Film with High Porosity and Broadband Light Absorption for Efficient Solar Steam Generation

Highlights Self-supporting Cu film with high porosity was obtained by dealloying of Al98Cu2. Nanoporous Cu (NP-Cu) film shows good hydrophilicity and strong broadband light absorption. NP-Cu film exhibits outstanding solar steam generation and desalination performance. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01063-z.


S1 Supplementary Figures and
. S1 Schematic of the SSG setup      As can be seen from Fig. S11, the evaporation efficiency of the NP-Cu-500 film also fluctuates little in 30 cycles under 1 sun illumination. On the whole, the range of evaporation efficiency of the NP-Cu-500 film is always lower than that of the NP-Cu film (Fig. 5h). And the average evaporation efficiency of the NP-Cu-500 film in 30 cycles is 90.1%, smaller than that of the NP-Cu film (92.4%). The result shows that the NP-Cu-500 film has good stability and durability. As can be seen from Fig. S13a, the ion concentration of Ca 2+ , K + , Mg 2+ and Na + in the seawater (Yellow Sea) decreases from 298.7, 307, 716, 6765 mg L -1 to 0.3, 0.3, 0.4, 6.7 mg L -1 respectively, which is greatly reduced after desalination. The collected water also meets the drinking water standards of the World Health Organization (WHO). And the NP-Cu-500 film also exhibits high ion rejections (Fig. S13b). These results indicate the NP-Cu-500 film has good seawater desalination ability.  NP-Cu film 0.0087 92.9 (under 1 sun) This work The cost of Cu is inherently low, and its high porosity (94.8%) further reduces the cost. Moreover, from the above comparison, the evaporation efficiency of the NP-Cu film with wick structure in this work is comparable to or even better than that of other noble metal-based SSG systems. In the case of similar evaporation efficiency, the NP-Cu film has a great cost advantage.

S2 Calculation of Porosity
The porosity of the NP-Cu film was calculated by the following equation, is the porosity, is the volume of the solid phase in the NP-Cu film, is the total volume of the NP-Cu film. The volume of the solid phase can be calculated by measuring the mass of the NP-Cu film combined with the metal density of pure Cu (8.96 g cm -3 ). Mass divided by density gives the volume of the solid phase. Taking one of the test data as an example, the mass of the NP-Cu film was 0.0073 g, thus the volume of the solid phase in the NP-Cu film was determined to be 8.15×10 -4 cm 3 . And the total volume of the NP-Cu film was 1.54×10 -2 cm 3 . Thus, the porosity of the NP-Cu film was determined to be 94.7%. The average of multiple sets of test results is 94.8%.

S3 Calculation of Heat Losses
In this work, the heat losses mainly include three ways, namely conduction heat loss, radiation heat loss and convection heat loss. The corresponding calculation process under one sun irradiation (1 kW m -2 ) is as follows.
(1) Conduction heat loss The heat conduction loss can be calculated by Fourier's law, where is the thermal conductivity of the cotton pillar (0.04 W m 1 K -1 ), is the sectional area of the cotton pillar (3.8×10 -5 m 2 ), ∆ ∆ is the gradient of temperature Nano-Micro Letter S8/S9 between the surface of the NP-Cu film and the bulk water, which was calculated to be around 329 K m -1 . is 1 kW m -2 and is the surface area of the NP-Cu film (4 cm 2 ). Thus, is 0.13%.
(2) Radiation heat loss The radiation heat loss can be calculated by Stefan-Boltzmann law, where is the emissive rate of the NP-Cu film (0.91, Fig. S15), is the Stefan-Boltzmann constant (5.67×10 -8 W m -2 K -4 ), is the radiative area (4 cm 2 ), 1 is the average temperature of the evaporation surface in the stable state (37 °C), 0 is the temperature of ambient environment near the NP-Cu film (28 °C). Thus, is 5.30%.
(3) Convection heat loss The convection heat loss can be calculated by Newton's law of cooling, where is the convection area (4 cm 2 ), ℎ is the convection heat transfer coefficient, which is assumed to be 5 W m -2 k -1 [S12]. Thus, the is 4.50%.
Based on the above results, the total heat loss of the NP-Cu film is around 9.93%.